1. Field of the Invention
The present invention relates to tow bars for connecting a vehicle to be towed to a towing vehicle and, more particularly without limitation, to tow bars for connecting to a pintle hitch of a towing vehicle.
2. Description of the Related Art
A tow bar is generally used for connecting a towing hitch arrangement of a vehicle to be towed, sometimes referred to herein as a towed vehicle, to a towing hitch arrangement of a towing vehicle. For applications wherein the towed vehicle will be towed at speeds other than very slow speeds, such as when a large airliner is being backed away from a terminal for example, the tow bar, which connects the front end of the towed vehicle to the rear end of the towing vehicle, generally has two tow bar legs, the front end of each tow bar leg separately and pivotally connected to a body portion of the tow bar. In use, the front ends of the tow bar legs form the apex of an isosceles triangle and the rear ends of the tow bar legs are spaced apart to form the sides of the isosceles triangle. The triangular configuration is intended to cause the towed vehicle to closely track the towing vehicle, both along straightaways and around corners.
Tow bars must generally be designed to accommodate variations in attitude that inherently occur between the towing and towed vehicles, which variations are constantly and continuously changing during use. One such variation in attitude between the vehicles occurs when the instantaneous elevation of the towing vehicle differs from the instantaneous elevation of the towed vehicle. A related variation in attitude between the vehicles occurs when the instantaneous ascent/descent orientation of the towing vehicle differs from the instantaneous ascent/descent orientation of the towed vehicle. Both of these related variations in attitude can be accommodated by apparatus designed to accommodate relative rotations between the towing and towed vehicles about a transverse, horizontal axis, sometimes referred to as the “pitch” axis.
Another such variation in attitude between the vehicles occurs when the instantaneous horizontal direction in which the towing vehicle is traveling differs from the instantaneous horizontal direction in which the towed vehicle is traveling, such as when the towed vehicle is being pulled around an unbanked corner for example. This situation, sometimes referred to as “yaw”, can be accommodated by apparatus designed to accommodate relative rotations between the towing and towed vehicles about a vertical axis.
Finally, another such variation in attitude between the vehicles occurs when the instantaneous sidewise tilt of the towing vehicle differs from the instantaneous sidewise tilt of the towed vehicle, such as the rocking motion which occurs when traversing uneven or rough pavement for example. This situation, sometimes referred to as “roll”, can be accommodated by tow bar apparatus designed to accommodate relative rotations between the towing and towed vehicles about a longitudinal, horizontal axis.
During actual towing procedures, all combinations of the pitch, yaw and roll are continuously occurring and constantly changing. Prior art is replete with tow bar designs that have been developed in an attempt to accommodate these phenomena, some of those designs being more successful than others. For example, a ball hitch/ball hitch receiver combination securing a tow bar to a towing vehicle can theoretically accommodate all three of the pitch, yaw and roll criteria. Although the ability of such a combination to accommodate yaw is acceptable and the pivot axes therefor are well-defined, unfortunately the ability of such a hitch combination to accommodate either pitch or roll is extremely limited. Failure to strictly observe such pitch and roll limitations can cause disastrous and even fatal results.
Another commonly used hitch arrangement involves using a conventional receiver hitch in combination with a conventional square hitch tube. Although such an arrangement may be convenient for connecting a tow bar to a towing vehicle, this type of connection by itself provides absolutely no ability to accommodate any one of the three pitch, yaw or roll criteria. As a result, the tow bar and/or connections between the tow bar and the towed vehicle must be relied upon to provide a solution for minimizing the potentially detrimental effects of pitch, yaw and roll.
Another arrangement that is useful, particularly when towing massive vehicles, such as heavy military equipment for example, comprises a pintle hitch of a towing vehicle connected to a lunette ring hitch. Such a pintle/lunette ring hitch arrangement substantially enhances the ability to accommodate pitch and yaw phenomena between the towing and towed vehicles. Unfortunately, this type of hitch arrangement inherently produces some play, although minimal, between the pintle and the lunette ring. As a result, neither the pitch axis nor the yaw axis are well-defined because the pintle continually shifts back and forth, and forwardly and rearwardly in the opening through the lunette ring. In so doing, the magnitude of the applied towing force is constantly differing between the two tow bar legs causing the connections to pivotally respond thereto which, in turn, causes the towed vehicle to wander or fishtail to a greater extent behind the towing vehicle than it would if the rotational axes between the pintle and lunette ring were well-defined. Such tendency to fishtail exacerbates wear and tear on the towing vehicle, on the towed vehicle, on the pintle, on the lunette ring, and on the pivotal connections between the tow bar legs and the tow bar body, which also visits greater stress on the operator of the towing vehicle while having to contend with such undesirable added activity between the towing and towed vehicles.
What is needed is a tow bar that counteracts the tendency of a towed vehicle to wander or fishtail which tendency operatively arises from the inherent play between a pintle and lunette ring hitch connection between towing and towed vehicles, such as a tow bar having tow bar legs that are operably maintained at an equiangular orientation relative to the body of the tow bar.